Mercury Molar Ratios Research Articles

Mercury exposure in ringed seals (Pusa hispida saimensis) in Lake Saimaa, Finland, and the placenta as a possible non-invasive biomonitoring tool

The Saimaa ringed seal (Pusa hispida saimensis) is a subspecies of ringed seal, landlocked in Lake Saimaa, Finland. The small population of less than 500 seals is facing many human-induced threats, including chemical contaminants. Mercury, in particular, has previously been suggested to be one of the chemicals affecting the viability of this endangered population. We analysed mercury concentrations from placentas and lanugo pup tissues (blubber, brain, kidney, liver, and muscle) to determine current prenatal exposure levels. These pups were found dead in or near birth lairs and were less than 3 months old. Additionally, we used threshold values available in the literature to estimate the potential mercury toxicity to the Saimaa ringed seal. We also determined selenium concentrations for its potential to alleviate the adverse effects of mercury. We further supplemented our study with brain samples collected from various seal age classes. These seals were found dead by either natural causes or by being caught in gillnets. The analysed chemicals were present in all tissues. For lanugo pups, mercury concentrations were the highest in the kidney and liver, whereas the highest selenium to mercury molar ratio was observed in placentas. The toxicity evaluation suggested that, in severe cases, mercury may cause adverse effects in lanugo and older pups. In these cases, the selenium concentrations were low and selenium to mercury ratio was below 1:1 threshold ratio and thus unlikely to provide adequate protection from the adverse effects of mercury. Furthermore, adverse effects are more likely to occur in adult seals, as mercury bioaccumulates, leading to higher concentrations in older individuals. Placental mercury concentrations correlated to those in the livers and muscle tissues of lanugo pups. This, together with the fact that placentas can be collected non-invasively and in good condition, provides a potential novel method for biomonitoring mercury exposure in Saimaa ringed seals.

Fish Tissue Mercury in Lakes and the Moderating Effects of Selenium

Fish mercury concentrations result in fish consumption advisories. However, selenium : mercury molar ratios >1 are protective to wildlife and humans. Therefore, we sampled total selenium (TSe) and total mercury (THg) concentrations and molar ratios in sport fish from 50 Idaho (ID) lakes >20 ha and 67 northeastern USA (NE) lakes >1 ha. Sample lakes were selected at random, to obtain unbiased estimates of mean fish tissue levels, with known confidence limits, for target populations of 95 ID lakes >20 ha in surface area and 12,557 NE lakes >1 ha. Bass and salmonids presented the greatest potential mercury toxicity risk to consumers based on their higher mercury content, desirability as game fish, and widespread distributions. Fish tissue THg exceeded safe consumption criteria in an estimated 20–80% of the lakes in the two regions and TSe exceeded safe consumption thresholds in an estimated 0–20% of the lakes in the two regions. However, the Se : Hg molar ratio was >1 in an estimated 90–97% of fish tested from NE and ID lakes. Therefore, we concluded that Se levels in these systems are usually sufficient to limit disruption of selenoprotein activities by Hg, and that fish consumption advisories based on Hg alone are unnecessarily restrictive.

Associations between total mercury, trace minerals, and blood health markers in Northwest Atlantic white sharks (Carcharodon carcharias)

The ecology and life-histories of white sharks make this species susceptible to mercury bioaccumulation; however, the health consequences of mercury exposure are understudied. We measured muscle and plasma total mercury (THg), health markers, and trace minerals in Northwest Atlantic white sharks. THg in muscle tissue averaged 10.0 mg/kg dry weight, while THg in blood plasma averaged 533 μg/L. THg levels in plasma and muscle were positively correlated with shark precaudal length (153–419 cm), and THg was bioaccumulated proportionally in muscle and plasma. Nine sharks had selenium:mercury molar ratios in blood plasma >1.0, indicating that for certain individuals the potential protective effects of the trace mineral were diminished, whereas excess selenium may have protected other individuals. No relationships between plasma THg and any trace minerals or health markers were identified. Thus, we found no evidence of negative effects of Hg bioaccumulation, even in sharks with very high THg.

Sources and trophic transfer of trace metals in wild fish from coastal areas in the South China Sea

Context Wild fish is a good source of minerals and other high-quality nutrition; however, many wild fish species potentially accumulate hazardous metals, making them a threat to human health. Aims The aim was to study characteristics and the source of metals in wild fish in the South China Sea by using, for the first time, the correlation of trace metals and stable isotopes. Methods Analytical instruments and statistical methods were respectively used to determine elements and the relative correlations. Key results Lead (Pb) and manganese (Mn) tended to accumulate in bluespot mullet and Macao tonguesole. Variation among fish species and spatial differences might be two important factors influencing both the metal concentrations and the selenium (Se):mercury (Hg) molar ratios in biota. Hg, Mn, Pb and tin (Sn) tended to be biomagnified with an increasing trophic level, whereas chromium (Cr) and copper (Cu) showed a trend of biodilution. Conclusions The Se:Hg molar ratios exhibited noticeable species and spatial variation for the wild fish, whereas the main sources of Sn and Pb contamination might be antifouling reagents and surface applications. Implications The speciation of the elements is worth investigating next, so as to obtain valuable insight into the state of the wild environment and the impacts to human wellbeing.

Essential and toxic elements in sustainable and underutilized seafood species and derived semi-industrial ready-to-eat products

Blue whiting (Micromesistius poutassou), pouting (Trisopterus luscus) and common dab (Limanda limanda) are underutilized fish species attractive in terms of sustainability. However, there is limited information about their nutritional characteristics as well as potential presence of environmental contaminants. Specimens caught in European waters were characterised for their content of essential and toxic elements. The three species, along with common carp and blue mussels, relevant for sustainable production too, were employed as raw materials for the development of semi-industrial ready-to-eat products. Calcium, copper, iodine, iron, selenium, zinc, cadmium, lead, mercury, and nickel were determined by ICP-MS, whereas methylmercury was determined by HPLC-ICP-MS. These two techniques were also used to determine arsenic and inorganic arsenic, respectively, in blue mussel and derived products. Differences in element contents were related to the biology and ecology of the examined species. Intake of nutrients and exposure to contaminants were assessed in relation to the relevant DRVs and HBGVs, respectively. All the species were found to be valuable dietary sources of selenium. Pouting was rich in iodine and mussels were good sources of iodine and iron. These two species had comparatively higher levels of mercury and lead, respectively. However, the levels of contaminants were generally of no concern in both raw materials and products. Iodine bioaccessibility was studied in blue whiting, a species with an intermediate iodine content, and found to be 98%. Selenium:mercury molar ratios were assessed and found to be favourable. The semi-industrial products were found to be good sources of selenium and many of them provided appreciable amounts of calcium, iron, copper and zinc.

Biomonitoring selenium, mercury, and selenium:mercury molar ratios in selected species in Northeastern US estuaries: risk to biota and humans.

The mutual mitigation of selenium and mercury toxicity is particularly interesting, especially for humans. Mercury is widely recognized as a pantoxic element; all forms are toxic to all organisms. Less well known is that selenium in excess is toxic as well. The high affinity between these elements influences their bioavailability and toxicity. In this paper, we use selected species from Barnegat and Delaware Bays in New Jersey to examine variations in levels of selenium and mercury, and selenium:mercury molar ratios between and within species. We report on species ranging from horseshoe crab eggs (Limulus polyphemus), a keystone species of the food chain, to several fish species, to fish-eating birds. Sampling began in the 1970s for some species and in the 1990s for others. We found no clear time trends in mercury levels in horseshoe crab eggs, but selenium levels declined at first, then remained steady after the mid1990s. Concentrations of mercury and selenium in blood of migrant shorebirds directly reflected levels in horseshoe crab eggs (their food at stopover). Levels of mercury in eggs of common terns (Sterna hirundo) varied over time, and may have declined slightly since the mid2000s; selenium levels also varied temporally, and declined somewhat. There were variations in mercury and selenium levels in commercial, recreational, and subsistence fish as a function of species, season, and size (a surrogate for age). Selenium:mercury molar ratios also varied as a function of species, year, season, and size in fish. While mercury levels increased with size within individual fish species, selenium levels remained the same or declined. Thus selenium:mercury molar ratios declined with size in fish, reducing the potential of selenium to ameliorate mercury toxicity in consumers. Mercury levels in fish examined were higher in early summer and late fall, and lower in the summer, while selenium stayed relatively similar; thus selenium:mercury molar ratios were lower in early summer and late fall than in midsummer. We discuss the importance of temporal trends in biomonitoring projects, variations in levels of mercury, selenium, and the molar ratios as a function of several variables, and the influence of these on risks to predators and humans eating the fish, and the eggs of gulls, terns. Our data suggests that variability limits the utility of the selenium:mercury molar ratio for fish consumption advisories and for risk management.

Interactions between Environmental Contaminants and Gastrointestinal Parasites: Novel Insights from an Integrative Approach in a Marine Predator.

Environmental contaminants and parasites are ubiquitous stressors that can affect animal physiology and derive from similar dietary sources (co-exposure). To unravel their interactions in wildlife, it is thus essential to quantify their concurring drivers. Here, the relationship between blood contaminant residues (11 trace elements and 17 perfluoroalkyl substances) and nonlethally quantified gastrointestinal parasite loads was tested while accounting for intrinsic (sex, age, and mass) and extrinsic factors (trophic ecology inferred from stable isotope analyses and biologging) in European shags Phalacrocorax aristotelis. Shags had high mercury (range 0.65–3.21 μg g–1 wet weight, ww) and extremely high perfluorooctanoic acid (PFOA) and perfluorononanoic acid (PFNA) residues (3.46–53 and 4.48–44 ng g–1 ww, respectively). Males had higher concentrations of arsenic, mercury, PFOA, and PFNA than females, while the opposite was true for selenium, perfluorododecanoic acid (PFDoA), and perfluooctane sulfonic acid (PFOS). Individual parasite loads (Contracaecum rudolphii) were higher in males than in females. Females targeted pelagic-feeding prey, while males relied on both pelagic- and benthic-feeding organisms. Parasite loads were not related to trophic ecology in either sex, suggesting no substantial dietary co-exposure with contaminants. In females, parasite loads increased strongly with decreasing selenium:mercury molar ratios. Females may be more susceptible to the interactive effects of contaminants and parasites on physiology, with potential fitness consequences.

Evaluating the concentrations of total mercury, methylmercury, selenium, and selenium:mercury molar ratios in traditional foods of the Bigstone Cree in Alberta, Canada

Traditional foods provide nutritional, social, and economic benefits for Indigenous communities; however, anthropogenic activities have raised concerns about mercury (Hg), especially methylmercury (MeHg), in these foods. This issue may be of particular concern for communities near large industrial activities, including the Bigstone Cree Nation adjacent to the Athabasca oil sands region, Canada. This community-led study sought to assess variation in THg and MeHg concentrations among traditional food types (plants or animals), species, and tissues (muscles, organs), and variation in concentrations of the micronutrient selenium (Se)— thought to protect against Hg toxicity—and Se:THg ratios. Thirteen plant and animal species were collected in 2015 by Bigstone Cree community members. We quantified THg, Se, and Se:THg ratios in 65 plant and 111 animal samples and MeHg in 106 animal samples. For plants, the lichen, old man’s beard (Usnea spp.), showed the highest concentrations of THg and Se (0.11 ± 0.02 and 0.08 ± 0.01 μg g−1 w. w., respectively) and also had a low Se:THg molar ratio. Concentrations of THg, MeHg, and Se differed among animal samples (P < 0.010), showing variation among species and among tissues/organs. Generally, concentrations of THg and MeHg were highest in aquatic animals, which also had relatively low Se:THg molar ratios. Overall results revealed substantial variation in the patterns of THg, MeHg, Se and Se:THg ratios across this comprehensive basket of traditional foods. Thus, measuring concentrations of THg alone, without considering MeHg and potential associations with Se, may not adequately convey the exposure to Hg in traditional foods.

Mercury and selenium concentrations, and selenium:mercury molar ratios in small cetaceans taken off St. Vincent, West Indies

This study measured the concentration of total mercury (THg) and selenium (Se), and calculated the Se:Hg molar ratios in the muscle, blubber, liver, and kidney of small cetaceans (false killer whale, Pseudorca crassidens; killer whale, Orcinus orca; Risso's dolphin, Grampus griseus; short-finned pilot whale, Globicephala macrorhynchus; and dolphins of the genus Stenella) taken for human consumption off St. Vincent, West Indies. Overall, 122 samples were analyzed; mean THg concentrations (μg/g dry weight) were highest in the liver (730), followed by the kidney (274), muscle (76.4), and blubber (4.57). To explain variability in muscle THg concentrations, carbon (δ13C) and nitrogen (δ15N) stable isotope ratios were analyzed to explore differences in dietary carbon source and relative trophic position, respectively, among species. There was no relationship between δ15N and THg concentration, but there was a positive relationship between δ13C and THg concentration. On average for each species, the Se:Hg molar ratios were >1 in blubber and <1 in muscle. All liver samples and the majority of kidney, muscle, and blubber samples exceeded the FAO/WHO human consumption advisory level of 1 μg/g wet weight. Based on our estimations, consuming only 6.6 g of muscle a week would exceed the MeHg provisional tolerable weekly intake of 1.6 μg MeHg/kg body weight/week for a 60 kg person. Given the high THg concentration in these cetaceans and the frequency at which these tissues are consumed, this is a potential human health issue that warrants further investigation.

Effects of geography and species variation on selenium and mercury molar ratios in Northeast Atlantic marine fish communities

Methylmercury (MeHg) is a potent neurotoxin that bioaccumulates in seafood. Co-occurrence of selenium (Se) may affect the bioavailability and toxicity of MeHg in organisms. Here we report the concentrations of total mercury (Hg) and Se in 17 teleost fish species (n = 8459) sampled during 2006–2015 from the North East Atlantic Ocean (NEAO) and evaluate species variation and effects of geography. Mean Hg concentration ranged from 0.04 mg kg−1 ww in Atlantic mackerel (Scomber scombrus) and blue whiting (Micromesistius poutassou) to 0.72 mg kg−1 ww in blue ling (Molva dypterygia). Se concentrations were less variable and ranged from 0.27 mg kg−1 ww in Atlantic cod (Gadus morhua) to 0.56 mg kg−1 ww in redfish (Sebastes spp.). The mean Se:Hg molar ratio ranged from 1.9 in blue ling to 43.3 in mackerel. Pelagic species had the lowest Hg concentrations and the highest Se:Hg ratios, whereas demersal species had the highest Hg concentrations and the lowest Se:Hg ratios. Se and Hg concentrations were positively correlated in 13 of the 17 species. Hg concentrations increased from the North to South in contrast to the Se:Hg molar ratio which exhibited the opposite trend. Fish from fjord and coastal areas had higher concentrations of Hg and lower Se:Hg molar ratios compared to fish sampled offshore. All species had average Se:Hg molar ratios >1 and Hg concentrations were largely below the EU maximum level of 0.5 mg kg−1 ww with few exceptions including the deep water species tusk (Brosme brosme) and blue ling sampled from fjord and coastal habitats. Our results show that two fillet servings of tusk, blue ling or Atlantic halibut (Hippoglossus hippoglossus) exceeded the tolerable weekly intake of MeHg although the surplus Se may possibly ameliorate the toxic effects of MeHg. However, some individuals with selenium deficiencies may exhibit greater sensitivity to MeHg.

The Shannon Entropy Trend of a Fish System Estimated by a Machine Vision Approach Seems to Reflect the Molar Se:Hg Ratio of Its Feed.

The present study investigates the suitability of a machine vision-based method to detect deviations in the Shannon entropy (SE) of a European seabass (Dicentrarchus labrax) biological system fed with different selenium:mercury (Se:Hg) molar ratios. Four groups of fish were fed during 14 days with commercial feed (control) and with the same feed spiked with 0.5, 5 and 10 mg of MeHg per kg, giving Se:Hg molar ratios of 29.5 (control-C1); 6.6, 0.8 and 0.4 (C2, C3 and C4). The basal SE of C1 and C2 (Se:Hg > 1) tended to increase during the experimental period, while that of C3 and C4 (Se:Hg < 1) tended to decrease. In addition, the differences in the SE of the four systems in response to a stochastic event minus that of the respective basal states were less pronounced in the systems fed with Se:Hg molar ratios lower than one (C3 and C4). These results indicate that the SE may be a suitable indicator for the prediction of seafood safety and fish health (i.e., the Se:Hg molar ratio and not the Hg concentration alone) prior to the displaying of pathological symptoms. We hope that this work can serve as a first step for further investigations to confirm and validate the present results prior to their potential implementation in practical settings.

Selenium: Mercury Molar Ratios in Freshwater Fish in the Columbia River Basin: Potential Applications for Specific Fish Consumption Advisories.

Fish provide a valuable source of beneficial nutrients and are an excellent source of low fat protein. However, fish are also the primary source of methylmercury exposure in humans. Selenium often co-occurs with mercury and there is some evidence that selenium can protect against mercury toxicity yet States issue fish consumption advisories based solely on the risks that methylmercury pose to human health. Recently, it has been suggested the selenium: mercury molar ratio be considered in risk management. In order for agencies to utilize the ratio to set consumption guidelines, it is important to evaluate the variability in selenium and mercury in different fish species. We examined 10 different freshwater fish species found within the Columbia River Basin in order to determine the inter- and intra-specific variability in the selenium: mercury molar ratios and the selenium health benefit values. We found significant variation in selenium: mercury molar ratios. The mean molar ratios for each species were all above 1:1, ranging from 3.42:1 in Walleye to 27.2:1 in Chinook salmon. There was a positive correlation between both mercury and selenium with length for each fish species apart from yellow perch and rainbow trout. All species had health benefit values greater than 2. We observed considerable variability in selenium: mercury molar ratios within fish species collected in the Columbia River Basin. Although incorporating selenium: mercury molar ratios into fish consumption holds the potential for refining advisories and assessing the risk of methylmercury exposure, the current understanding of how these ratios apply is insufficient, and further understanding of drivers of variability in the ratios is needed.

Mercury Hazard Assessment for Piscivorous Wildlife in Glacier National Park

Abstract We examined the mercury hazard posed to selected piscivorous wildlife in Glacier National Park (GNP), Montana. Logging Lake was our focal site where we estimated the dietary mercury concentrations of wildlife (common loon [Gavia immer], American mink [Neovison vison], river otter [Lontra canadensis], and belted kingfisher [Megaceryle alcyon]) by assuming that fishes were consumed in proportion to their relative abundances. To evaluate if Logging Lake provided a suitable baseline for our study, we made geographic comparisons of fish mercury levels and investigated the distribution and abundance of high mercury fishes within GNP. We complimented our assessment by examining selenium:mercury molar ratios in fishes from Logging Lake and Saint Mary Lake. Our results suggest fish consumption does not imperil wildlife from Logging Lake based on published thresholds for adverse mercury effects, but some hazard may exist particularly if there is strong feeding selectivity for the most contaminated species,...

The levels of mercury, methylmercury and selenium and the selenium health benefit value in grey-eel catfish (Plotosus canius) and giant mudskipper (Periophthalmodon schlosseri) from the Strait of Malacca

The present study examined the concentrations of mercury (Hg), methylmercury (MeHg), and selenium (Se) in the multiple tissues of the Plotosus canius and Periophthalmodon schlosseri collected from the Strait of Malacca. The mean value in mg kg−1 of Hg (P. canius: 0.34 ± 0.19; P. schlosseri: 0.32 ± 0.18) and MeHg in muscle (P. canius: 0.14 ± 0.11; P. schlosseri: 0.17 ± 0.11) were below the Codex general standard for contaminants and toxins in food and feed (CODEX STAN 193-1995), the Malaysian Food Regulation 1985 and the Japan Food Sanitation Law. For P. canius, the liver contained the highest concentrations of Hg (0.48 ± 0.07 mg kg−1) and MeHg (0.21 ± 0.00 mg kg−1), whereas for P. schlosseri, the gill contained the highest concentrations of Hg (0.36 ± 0.06 mg kg−1) and MeHg (0.21 ± 0.05 mg kg−1). The highest concentration of 80Se (mg kg−1) was observed in the liver of P. canius (20.34 ± 5.68) and in the gastrointestinal tract (3.18 ± 0.42) of P. schlosseri. The selenium:mercury (Se:Hg) molar ratios were above 1 and the positive selenium health benefit value (HBVSe) suggesting the possible protective effects of Se against Hg toxicity. The estimate weekly intakes (EWIs) in μg kg−1 body weight (bw) week−1 of Hg (P. canius: 0.27; P. schlosseri: 0.15) and MeHg (P. canius: 0.11; P. schlosseri: 0.08) were found to be lower than the provisional tolerable weekly intake established by the Joint FAO/WHO Expert Committee on Food Additives (JECFA). Based on the calculated EWIs, P. canius, and P. schlosseri were found to be unlikely to cause mercury toxicity in human consumption.

Analysis of mercury and methylmercury concentrations, and selenium:mercury molar ratios for a toxicological assessment of sperm whales (Physeter macrocephalus) in the most recent stranding event along the Adriatic coast (Southern Italy, Mediterranean Sea)

Mass stranding of sperm whales (Physeter macrocephalus) is a rare event in the Mediterranean Sea. In September 2014, a pod of seven sperm whales became stranded along the Adriatic coast of Southern Italy. This is the seventh occurrence of this type since 1555 in this sea basin.Total concentrations of mercury (T-Hg), methylmercury (MeHg) and selenium (Se) were measured from brain, muscle, liver and kidney of three female sperm whales, which died in this event.Analyses showed considerable, age-dependent variations in Hg and Se concentrations in the different organs. The contamination levels of T-Hg in the liver (up to 200mgkg−1) and brain (up to 21mgkg−1) samples were markedly higher than those in the kidney and muscle samples. The liver and brain also showed the highest Se levels. Se:Hg molar ratios ⩾1 were observed in all the organs of the three sperm whales, suggesting that Se could protect the animals from Hg toxicity. The risk of Hg-associated neurotoxicity was assessed by comparing our values to thresholds set for neurotoxicity in mammals, and the role of Se in the detoxification process of T-Hg/MeHg is discussed herein.

Selenium and mercury molar ratios in commercial fish from the Baltic Sea: Additional risk assessment criterion for mercury exposure

BackgroundMercury content in fish poses risks to the fish and to those who consume them. The aim of the current study was to verify the protective role of selenium against toxic mercury in Baltic fish. The assessment criteria were the Se:Hg molar ratio, its variability depending on species and tissue, and correlations among Se:Hg ratios, mercury concentration, and specimen length. Assays were performed in muscle and liver tissues of Baltic Sea commercial fish species, i.e., cod, herring, sprat, plaice, and turbot. ResultsMercury concentrations in fish from the Baltic Sea are at low level. The values of the Se:Hg molar ratio were higher than 1 (with the exception of a few cod specimens), with ranges in muscle tissues as follows: cod 0.75–28.2; herring 2.0–50.3; sprat 14.2–56.2; flatfish 1.5–35.1; and in livers as follows: cod 10.9–268.2; herring 10.7–87.1; flatfish 10.2–232. The values of the Se:Hg ratio in muscle and liver tissues were negatively correlated with mercury content and specimen length. ConclusionMercury concentrations in commercial fish from the Baltic Sea are low and do not pose risks to consumers. The high values of the Se:Hg molar ratio confirm that mercury levels are safe, and also that selenium might offer protection against methylmercury toxicity, which could increase the safety of fish consumption. The values of the Se:Hg molar ratio could be an additional criterion, in addition to measuring Hg concentrations, for evaluating the risk of mercury exposure in fish from the Baltic Sea.

Interspecific and locational differences in metal levels in edible fish tissue from Saudi Arabia.

Metal levels in fish have been extensively studied, but little data currently exists for the Middle East. We examined the levels of metals and metalloids (aluminum, arsenic, copper, manganese, selenium, zinc, and mercury) in the flesh of 13 fish species collected from three fishing sites and a local fish market in Jeddah, Saudi Arabia. We tested the following null hypotheses: (1) there are no interspecific differences in metal levels, (2) there are no differences in metal levels in fishes between market and fishing sites, (3) there are no size-related differences in metal levels, and (4) there are no differences in selenium:mercury molar ratio among different fish species. There were significant interspecific differences in concentrations for all metals. There was an order of magnitude difference in the levels of aluminum, arsenic, mercury, manganese, and selenium, indicating wide variation in potential effects on the fish themselves and on their predators. Fishes from Area II, close to a large commercial port, had the highest levels of arsenic, mercury, and selenium, followed by market fishes. Mercury was positively correlated with body size in 6 of the 13 fish species examined. Mercury was correlated positively with arsenic and selenium, but negatively with aluminum, cobalt, copper, manganese, and zinc. Selenium:mercury molar ratios varied significantly among species, with Carangoides bajad, Cephalopholis argus, Variola louti, and Ephinephelus tauvina having ratios below 10:1. These findings can be used in risk assessments, design of mercury reduction plans, development of fish advisories to protect public health, and future management decision-making.

Metals in tissues of migrant semipalmated sandpipers (Calidris pusilla) from Delaware Bay, New Jersey

There is an abundance of field data on levels of metals for feathers in a variety of birds, but relatively few data for tissues, especially for migrant species from one location. In this paper we examine the levels of arsenic, cadmium, chromium, lead, manganese, mercury and selenium in muscle, liver, brain, fat and breast feathers from migrant semipalmated sandpipers (Calidris pusilla) collected from Delaware Bay, New Jersey. Our primary objectives were to (1) examine variation as a function of tissue, (2) determine the relationship of metal levels among tissues, and (3) determine the selenium:mercury molar ratio in different tissues since selenium is thought to protect against mercury toxicity. We were also interested in whether the large physiological changes that occur while shorebirds are on Delaware Bay (e.g. large weight gains in 2–3 weeks) affected metal levels, especially in the brain. There were significant differences among tissues for all metals. The brain had the lowest levels of arsenic and cadmium, and was tied for the lowest levels of all other metals except lead and selenium. Correlations among metals in tissues were varied, with mercury levels being positively correlated for muscle and brain, and for liver and breast feathers. Weights vary among individuals at the Delaware Bay stopover, as they arrive light, and gain weight prior to migration north. Bird weight and levels of arsenic, cadmium, and selenium in the brain were negatively correlated, while they were positively correlated for lead. There was no positive correlation for mercury in the brain as a function of body weight. The selenium:mercury molar ratio varied significantly among tissues, with brain (ratio of 141) and fat having the highest ratios, and liver and breast feathers having the lowest. In all cases, the ratio was above 21, suggesting the potential for amelioration of mercury toxicity.

Selenium:mercury molar ratios in bullfrog and leopard frog tadpoles from the northeastern United States.

Vertebrates experience adverse effects from methylmercury, largely obtained through their food. Selenium has the potential to reduce the toxic effects of methylmercury (and vice versa). In this paper, we examine the selenium:mercury molar ratios in tadpoles (Lithobates sphenocephalus, Lithobates catesbeianus (formerly Rana), and a newly documented leopard frog species currently referred to as R. sp. nov.) and fully formed leopard frog metamorphs. There were no significant differences in metal levels between the two leopard frog species, and data were therefore combined. Selenium:mercury molar ratios varied from 19 to 38 for bullfrog tadpoles, from 16 to 330 for leopard frog tadpoles, and from 7 to 17 for leopard frog metamorphs. Leopard frog tadpoles with less than 45days exposure to field conditions had significantly higher molar ratios than other tadpoles and leopard frog metamorphs. There were significant locational differences for the molar ratios of bullfrogs, and leopard frog tadpoles with more than 45days of field exposure. At the sites where we were able to sample both leopard frog tadpoles and leopard frog metamorphs, there were significant differences between the two distinct life stages. Most of the variation in the ratio was accounted for by selenium levels, field sites, and exposure period.

In situ stabilization of entrapped elemental mercury

Elemental mercury is a dense immiscible fluid which gets entrapped as residual mercury in the pore spaces of the subsurface during improper disposals and accidental spills. This paper investigates in situ stabilization of entrapped elemental mercury to mercury sulphide using aqueous sodium polysulphide solution. Batch experiments showed 100% conversion efficiency of elemental mercury to mercury sulphide in a period of 96 h with sodium polysulphide/elemental mercury molar ratio of 1. XRD analysis identified the precipitate formed as mercury sulphide. Micromodel experiments, with glass beads as porous media, further demonstrated in situ stabilization of entrapped mercury under different residual mercury saturations. It was found that in a period of 10 days, 10% of entrapped mercury was stabilized as mercury sulphide, 0.088% was removed as dissolved mercury and the remaining elemental mercury was retained in porous media encapsulated by the newly formed mercury sulphide precipitate. However, there was no leaching of mercury from the micromodel effluent once stabilization was achieved.